Instrument lubricating oil



No Drawing. Filed Sept. 1, 1960, Ser. No. 53,351 8 Claims. (Ci. 252-33.4)

The present invention relates to the field of lubricants generally and, more particularly, to improved lubricating Compositions adapted to the lubrication of fine instruments and delicate mechanisms such as those employed in Watches, clocks, meters, weather recording instruments, galvanometers, aircraft instruments, scientific instruments, shell fuses, ordnance fire control and gun directing equipment, and the like, and small motors and compressors, especially those used as aircraft accessories, such as air compressors, electric motors, refrigeration equipment and similar apparatus.

Lubricating compositions in the nature of those of the present invention must possess special characteristics in order to adequately and fully meet the special requirements of delicate mechanisms and motors. Such oils should possess a pour point below -30 F. and preferably below 60 F. Their flash points should be above 300 F. and preferably above 365 P. so as to eliminate the fire hazard arising from the use of more volatile oils and to minimize loss by evaporation over prolonged periods, particularly in air or gas turbine driven instruments such as gyro compasses, supercharger mechanisms, etc. Such oils should be chemically stable, particularly against the action of atmospheric oxygen in the presence of metals in use and during storage so as not to become gummy or corrosive due to the formation of acidic bodies after long periods of use. Temperatures during storage and operating conditions may vary from 70 to +250 F. Also such oils should show good adherence to metals but should not creep or spread.

The need for the lubricant having a low pour point, particularly with regard to the lubrication of aircraft instruments, which are often subjected to extremely low temperatures in the air, is manifest. Ordinary atmospheric temperatures, that is, ground level temperatures, vary over a rather wide range becoming at times excessively high, particularly in the tropics so that an oil to meet these conditions must be sufficiently viscous at these higher temperatures that it will not drain or flow from the bearing being lubricated. n the other hand, it must not be so thick as to interfere with the movements of instrument components at temperatures extending down to 70 F. which may be encountered at high altitudes in the troposphere. Many instruments and motors are so constructed and encased that it requires the services of a specially trained expert to service them. Such servicing is supplied only periodically and often after the lapse of a considerable period of time, which may be up to several years. Lubricants designed for this type of service must be capable of meeting all of these strict qualifications.

An additional essential characteristic of a good instrument oil is that it be non-corrosive to metals. This aspect assumes great importance since, as mentioned, the oils may be in the instrument for a period of years. Also, the

3,fi9il,752 Patented May 21, 1953 portions lubricated will, in general, comprise very small finely machined metallic components. It would require only an infinitesimal amount of corrosion of these parts to seriously affect the accuracy of the entire instrument. Therefore the oil must be non-corrosive to any of the metals commonly used in precision instruments, such as copper, magnesium, aluminum, steel, cadmium and the like.

In addition, it is important (1) that in service a desirable instrument oil not change appreciably in viscosity, (2) that it does not evaporate appreciably at the highest temperatures encountered, (3) that it does not form precipitates, get cloudy or hazy in use or in storage, and (4) that it does not become acidic.

Various compositions are known and have been described in the literature as suitable for precision instrument lubrication. These compositions run the gamut from highly refined mineral oils to synthetic lubricants such as silicoues, diesters and complex esters. Of these, the diesters have a majority of the properties required of a good instrument oil, that is, they have to a greater degree the properties already described. Even thouh the diesters per se have many desirable properties for instrument oils, better characteristics are obtained When various diesters are blended toegther in varying proportions. This blending is particularly appropriate when it is desired that the oils have certain viscosity characteristics. The blends are further improved with various additives. The armed forces, in particular, have a large need for a large variety of instruments which are to be used in a multitude of applications. For example, the military is the recipient of the most advanced aircraft designs, which usually will increase the severity of conditions to which aircraft instruments will be exposed. Therefore, military specifications for instrument oils are considered to be a criteria which only an exceptional instrument oil can meet in every respect.

The present invention resides in the discovery of a particular blended lubricating composition which meets or excels every portion of the specification MIL-L- 6085A, Amendment 2 for instrument oils. In addition, such a lubricating composition has been found to be compatible with Freon gas which is used in many compressors and in refrigeration equipment. As many other lubricants form a precipitate in the presence of Freon, such compatibility extends the utility of the lubricant of the invention over a broad area.

The lubricating composition of the invention comprises a major proportion of synthetic diesters, 2 to 15, e.g. 3 to 7, wt. percent of a metal sulfonate and 0.1 to 1.0, elg. 0.3 to 0.8, wt. percent of a phenol, said blend having a viscosity at 65 F. of not more then 12,000 centistokes and a viscosity at F. of at least 8 centistokes.

Synthetic diesters of the invention are prepared from dicarboxyhc acids which are fully esterified with monohydric alcohols, or from glycols fully esterified with monocarboxylic acids. The total number of carbon atoms in the diester molecule is about 20 to 36, preferably 22 to 30. Preferred dicarboxylic dieesters are those of the formula ROOCR'COOR branching in thehydrocarbon chain of the x0 alcohols.

resultsin diester oils having low pour points and low viscosities at the lower temperatures. These alcohols are prepared from olefins, such as polymers and copolymers of C and C monoolefins, which are reacted with carbon monoxide and hydrogen in the presence of a cobalt-containing catalyst, such as a cobalt carbonyl catalyst, at temperatures of about 300 to 400 F., and under pressures of about 1,000 to 3,000 p.s.i. to form aldehydes. The resulting aldehyde product is then hydrogenated to form the alcohol which is then recovered from the hydrogenation product.

The metal sulfonates which can be used in this invention are the oil-soluble alkaline earth metal, e.g. barium, salts of high molecular weight sulfonic acids, i.e. sulfonic acids, having a molecular weight of 200 to 800, e.g. 200 to 600. Such sulfonates may be derived by the treatment of petroleum oils of the lubricating oil range with fuming sulfuric acid as is well known to the art and as described in numerous patents, e. g., US. 2,467,- 176; The sulfonates can also be derived from relatively pure alkyl aryl sulfonic acids having from about 10 to 33 carbon atoms per molecule. For example, sulfonated products of alkylated aromatics such as benzene, toluene, xylene, etc. alkylated with olefins or olefin polymers of the type of polypropylene, polyisobutylene, etc. can be used. Specific examples of sulfonates which are used as additives include: petroleum sulfonates such as calcium petroleum sulfonate and barium petroleum sulfonate; and synthetic sulfonates such as calcium di-C alkyl benzene sulfonate, barium di-C alkyl benzene sulfonate and calcium C alkyl benzene sulfonate, wherein said 0,, alkyl group is derived from diisobutylene; said C group is obtained from tripropylene and said C group is obtained from tetraisobutylene.

The phenols usable in the invention may be any aromatic nuclear alcohol including mono-, dior tri-hydric phenols, substituted phenols such as C to C e.g., C to C alkyl and alkoxy substituted phenols, bis-phenols and the like. Examples of such phenols include: phenol, 2,4,6,tri-t-butyl phenol; 2,4,methyl-6-t-butyl phenol; 2-tbutyl-4-methox-y phenol; 3-t-butyl-4 methoxy phenol; 2,2 methylene bis(4-methyl,6-t-butyl) phenol; alphanaphthol, beta-naphthol, cathechol, resorcinol, etc. 2-6- (Eli-tertiary butyl-p-cresol is preferred.

The diesters, sulphonates, and phenols of the instrument oil will be blended in such a manner that the viscosity of the oil will be not more than 12,000 centistokes at -65 F. and not less than 8.0 centistokes at 130 F.

Preferably, the diester portion of the instrument oil will comprise a blend of three difierent esters, namely: 45 to 65 wt. percent of the diester formed irom a C to C alcohol and a C to C dicarboxylic acid and 35 to 55 wt. percent of a mixture of diesters, said mixture comprising 60 to 40 wt; percent of a diester formed from a C to C alcohol and a C to C dicarboxylic acid and 40 to 60 wt. percent of a diester formed from a C to C alcohol and a C to C dicarboxylic acid.

:Particularly preferred proportions of the diesters are: 50 to 65 wt. percent of the diester formed from a C to C alcohol and a C to C carboxylic acid and 35 to 50 wt. percent of a mixture of diesters, said mixture comprising 55 to 45 wt. percent of a diester formed from a C to C alcohol and a C to Cq dicarboxylic acid and 45 to 55 wt. percent of a diester formed from a C to C alcohol and a C to C dicarboxylic acid. 'It is preferred that the alcohol portion of the two diesters of the mixture be an Oxo alcohol and the alcohol portion of the other diester be not as highly branched as an 0x0 alcohol. These weight percents are based on the entire instrument oil compositions without additives.

Various other conventional additives may also be added to the compositions of the invention. Examples of such additives include: detergents, viscosity index improvers, corrosion inhibitors, pour depressants, dyes and the like.

In order to more fully illustrate the invention, the following preferred blend was prepared and subjected to the tests of MlL-L-6085A, which is referred to herein as the specification.

EXAMPLE I;

Ingredients: Percent weight Barium sulfonate 5.0 2-6-di-tertiary butyl-p-cresol 0.5 Dl-Cg OX0 adipate 20.0 Di-C Oxo adipate 20.0 Di-Z-ethyl hexyl sebacate 54.5

45% in a solvent extracted naphthenlc pale oil having a. viscosity at F. of about 102 SUS.

Preparation: All the ingredients were charged to a fivegallon, open head drum and thoroughly mixed. The resultant blend was then filtered and was ready for use.

Tests and Test Results-Example I The following tests according to the specification were performed on samples drawn from the 20 gallon batch instrument oil of Example *1.

Test 1.--L0w Temperature Stability Test at -65- F.

r for 72 Hours The procedure for this test was to place a 100 ml. sample of the instrument oil in a clear glass 4-ounce container. The container was stoppered and placed in a cold box which was maintained at a temperature of 65 F. for seventy-two hours. At the end of this time the sample was removed and examined visually for evidence of gelling, separation or crystallization. To pass this test there should be no such gelling, separation or crystallization. All of the Example I samples passed.

Test 2.Evaporation after 22 Hours at 210 F. (Volatility) The procedure of this test comprised taking a IO-gram sample in an evaporation dish .made of aluminum foil having a 2% inch inside diameter and a /8 inch depth. The dishes were then placed in a gravity conduction air oven maintained at 210 F. to 1 F. for a period of 22 hours. The dishes were then removed, cooled and re- Weighed. The loss of weight of the oil in percent of the original samples was 0.67%. The specification requires that there be not more than 1.00% evaporation loss.

Test 3.Humidity Cabinet Test for Corrosion I spots of between 1 and 2 millimeters maximum diameter.

To be acceptable, 4 out of 5 panels must pass the test. All five of the panels tested passed the test.

Test 4.-Galvanic Corrosion Three steel disks each with one polished side were coated with the oil of Example I by dipping a stirring rod in the oil and allowing the oil from the rod to drop on the polished side of each disk. The drops were spread so as to completely coat the disk. Brass clips were then clamped over the coated disks. The three assemblies were then placed in a test chamber which was maintained at 80 F. and 50% relative humidity for a period of days. The assemblies were removed and the clips taken ofi each disk. The portions of the disks under the brass clips were then examined under 10X magnification. In order to pass the test the brass-contacted areas of at least 2 out of the three disks should show no evidence of corrosion, pitting or other attack. The other disk may show no more than three spots Within the brasscontacted area. All three of the disks tested with the oil of Example I showed no corrosion, pitting or other attack.

Test 5 .Precipitati0n Number A 10 ml. sample of the Example I oil was placed in the special graduated centrifuge tube. Then 90 milliliters of precipitation naphtha was added to the tube and the oil temperature was raised to about 90-95" F. The tube was then whirled at 1500 r.p.m. for 10 minutes. The tube was removed and the volume of sediment at the bottom of the tube was checked. This was repeated four times. :No sediment at all was obtained. This conforms with the specification which calls for a precipitation number of 0.

Test 6.-0xidati0n Corrosion Test Five metal plates, i.e. copper, magnesium alloy, aluminum alloy, steel, and cadmium-plated steel of known area and weight were heated for 168 hours at 250 F. in an oil sample with regulated air blowing. The metal plates were then removed and the weight change per square centimeter was calculated. The specification requires that there be no more weight change than :02 mg. per square centimeter for each plate and there be no pittings, etchings or corrosion. Slight discoloration of the copper is permitted. All five plates met the requirements of the specification.

The viscosity of the oil after the test was determined to be 8.22 cs. at 130 F. compared with 8.21 cs. at 130 F. before the exposure to the panels. This amounts to a viscosity increase of about 0.10%. The neutralization number after exposure was 0.03 compared with 0.02 before exposure which amounted to an increase of 0.01. The evaporation loss during the course of the test was 0.65% and the oils appearance was a clear yellow. The weight losses of the metal plates were all well within the limit of the specification.

In addition to the above tests, several other tests which are well known conventional tests were also performed on the oil of Example I. In addition to these tests it was further observed that a sample of the Example I oil stored at ambient temperature for a year was clear and bright; no precipitate or cloud formed. The results of all the tests are summarized in Table I.

As can be seen on this table the instrument oils of the invention meet the specification or exceed it in every particular. These lubricating oils thus can be considered as outstanding instrument type oils.

EXAMPLE II In order to illustrate the utility of the lubricating oils of the invention, the oil of Example I is used to lubricate a watch, by placing several drops in the works of the watch.

EXAMPLE III In order to illustrate the utility of the instrument lubricating oils of the invention, particularly in regard to instruments that undergo a wide range of temperature change, aircraft instruments are lubricated with the oil of Example I.

6 EXAMPLE IV In order to illustrate the utility of the lubricating oils of the invention, particularly in regard to compressors, a compressor having Freon gas is lubricated with the oil of Example I.

TABLE I.-TEST RESULTS MILL-6085A Test EX-I Low temp. stabil. test at Pass No gelling, separa- 65F. for 72 hours. tion or crystallization. Vggosig at 65F., ASTM 10,510 cs 12,000 max. Evaporation, 22 hrs. at 1.0% max.

210F. Flash point ASTM #D-QZ..- 365 F. min. Corrosion, hrs/5 panels Perfect Pass (4 out 5).

(humidity cabinet). Galvanic corrosion, 3 specido. Pass (2 out 013).

mens. Color, #ASTM union color- Less than 1 5 max.

meter. Appearance Clear, transparent"- Pour point ASTM #D97 -85 F 70 F. min. Precipitation number Pass 0. Oxidation corrosion test:

Viscosity at F.:

before. 8.0 es. min. after Neut. numbe Before After Percent viscosity change. $5.0. Neut. number increase- 0.5 max Percent oil loss 0 65 Appearance Weight loss, metal:

M 0.002.. ;4;0 2 max. Al 0.000-- $0.2 max. Cu 0.038.- =l=(l.2 max. Cd 0.031 5 0.2 max. Steel 0.015 5:02 max.

1 Unusual terminology reserved for only the most perfect panels.

What is claimed is:

1. A lubricating composition suitable for use as an instrument lubricant having a viscosity of less than 12,000 cs. at 65 F. and more than 8 cs. at 130 F., a flash point above 365 F., and a pour point lower than -70 R, which comprises 2 to 15 wt. percent of an alkaline earth metal sulfonate, 0.1 to 1.0 wt. percent of a phenol which can be substituted with a maximum of 4 substituents selected from the group consisting of C to C alkyl radicals and C to C alkoxy radicals, and a major proportion of a diester blend, said diester blend comprising (1) 50 to 65 wt. percent of a diester of a C to C monohydric saturated alcohol and a C to C dicarboxylic acid, and (2) 30 to 50 wt. percent of a mixture of diesters, said mixture comprising (a) 55 to 45 wt. percent of a diester of a C to C monohydric saturated alcohol and a C to C dicarboxylic acid, and (b) 45 to 55 wt. percent of a diester of a 'C to C monohydric saturated alcohol and a C to C dicarboxylic acid.

2. A lubricating composition according to claim 1 wherein said alkaline earth metal is barium.

3. A lubricating composition according to claim 1 wherein said phenol is 2-6-di-tertiary butyl-p-cresol.

4. A lubricating composition according to claim 1 wherein said diester of a C to C alcohol is di-(C Oxo) adipate, said diester of a C to C alcohol is di-(C Oxo) adipate and said diester of a C to C alcohol is di-(2- ethyl hexyl) sebacate.

5. A lubricating composition suitable for use as an instrument lubricant and having a viscosity of less than 12,000 cs. at 65 F. and more than 8 cs. at 130 F., a flash point above 365 F, and a pour point lower than 70 R, which comprises 2 to 15 wt. percent of barium sulfonate, 0.1 to 1.0 wt. percent of 2-6-di-tertiary butylp-cresol and a major proportion of a diester blend com? prising 50 to 65 Wt. percent of di-(2-ethy1 hexyl) sebacate and 35 to 50 wt. percent of a mixture of diesters said mixture comprising 55 to 45 wt. percent of di-(C Oxo) adipate and 45 to 55 wt. percent of (ii-(C3 Oxo) adipate.

6. A lubricating composition suitable for use as an instrument'lubricant having a viscosity of less than 12,000 cs. at 65 F. and more than 8 cs. at 130 F.,' a flash point above 365 F, and a pour point lower than -70 R, which comprises about 5.0 wt. percentof barium sulfonate; about 0.5 wt. percent of Z-G-di-tertiary butyl-pcresol; and a major proportion of a diester blend comprising about 54.5 wt. percent of di-(Z-ethyl hexyl) sebacate and about 40% of a mixture of diesters, said mixture comprising about 50% of di-(C 0x0) adipate and about 50 Wt. percent of di-(C Oxo) adip-ate.

7. A method of lubricating relatively moving surfaces which comprises coating said surfaces with the lubricating composition of claim 1.

8. A method of lubricating relatively moving surfaces which comprises coating said surfaces with the lubricating composition of claim 5.

References Cited in the file of this patent UNITED STATES PATENTS Branched-Chain Diesters, in Industrial and Engineering Chemistry, vol. 39, No. 4, pp. 484 to 491, April 1947. McTurk: Synthetic Lubricants, W.A.D.C. Technical Report 53-88 AD No. 27520, October 1953, pp. 10 and 50 relied on. 

1. A LUBRICATING COMPOSITION SUITABLE FOR USE AS AN INSTRUMENT LUBRICANT HAVING A VISCOSITY OF LESS THAN 12,000 CS. AT -65* F. AND MORE THAN 8 CS. AT 130* F., A FLASH POINT ABOVE 365* F., AND A POUR POINT LOWER THAN -70* F., WHICH COMPRISES 2 TO 15 WT. PERCENT OF A PHENOL EARTH METAL SULFONATE, 0.1 TO 1.0 WT. PERCENT OF A PHENOL WHICH CAN BE SUBSTITUTED WITH A MAXIMUM OF 4 SUBSTITUENTS SELECTED FROM THE GROUP CONSISTING OF C1 TO C5 ALKYL RADICALS AND C1 TO C5 ALKOXY RADICALS, AND A MAJOR PROPORTION OF A DIESTER BLEND, SAID DIESTER BLEND COMPRISING (1) 50 TO 65 WT. PERCENT OF A DIESTER OF A C6 TO C10 MONOHYDRIC SATURATED ALCOHOL AND A C3 TO C12 DICARBOXYLIC ACID AND (2) 30 TO 50 WT. PERCENT OF A MIXTURE OF DIESTERS, SAID MIXING COMPRISING (A) 55 TO 45 WT. PERCENT OF A DIESTER OF A C9 TO C11 MOMOHYDRIC SATURATED ALCOHOL AND A C5 TO C7 DICARBOXYLIC ACID, AND (B) 45 TO 55 WT. PERCENT OF A DIESTER OF A C6 TO C8 MONOHYDRIC SATURATED ALCOHOL AND A C5 TO C7 DICARBOXYLIC ACID. 